Resource Person: Dr. Minu Joy, Alphonsa college, Pala

**Project Title:**

**Primordial Non - Gaussianity**

**Onset:**

** ** The standard model of cosmology provides a consistent picture of the origin and evolution of the universe. Nevertheless, the cosmologists are looking for a precise and complete understanding of the first moments and fate of the universe. The primordial perturbations [Mukhanov & Chibisov 1982, Starobinsky 1982], originated as quantum fluctuations during the inflationary expansion of the universe [Guth 1981, Linde 1982] are manifested today by the anisotropies in the cosmic microwave background (CMB) and are characterized in terms of the power spectra. The power spectra of both the CMB and the large scale structure of the observable universe have evolved from a common primordial spectrum of curvature perturbations and the observation of these spectra provide a unique opportunity to determine the more detailed properties of inflation. For the reliable comparison of inflationary predictions and observational data we need precise analytical studies that can meet the accuracy of the observations.

The existing CMB and other observational data are approaching the level of accuracy necessary to detect deviations from exact scale invariance of the spectrum and to distinguish between different inflationary scenarios. The recent data from the Wilkinson Anisotropy Probe (WMAP) suggest a non zero value of the running of the spectral index [Spergel *et al. *2007, Hinshaw *et al*. 2008] and also the existence of local spikes at some low *l* values which may indicate that inflationary properties may be more complex than the existing simple paradigms. In nutshell, the traditional methods for the theoretical calculation of the primordial power spectrum do not meet the accuracy goal of much anticipated *Planck* . Hence the call for more accurate modelling of the inflationary scenario has arisen.

One of the generic predictions from inflationary scenario is that the primordial fluctuations are exactly Gaussian in linear order; however, the non-linearity in the inflaton will produce weak non-gaussianity. Thus measuring the non-gaussianity in the CMB radiation anisotropy is a probe of the non-linear physics in the very early universe and also it would be a significant challenge to the currently favoured models of the early universe.

**Background**** **: General Relativity, Cosmology, Quantum Field Theory

**Background reading** :

**(a) General**

1. First three minutes - Steven Weinberg

3. Quantum Field Theory in Curved Space-Time - Birrel & Davies

** (b) Topic**

1. Early Universe - Kolb & Turner

2. Cosmological Inflation and Large Scale structure - Liddle &Lyth

3. Spergel D. N., Bean R. and Dor ́ O. et al., Astroph. J. Suppl. 170, 377 (2007)

** Please click Here for the presentation **